1. Field of the Invention
The invention is directed to a drive unit with an internal combustion engine coupled to a driven shaft and a reciprocating piston expansion engine operatively coupled to a crankshaft, wherein the driven shaft is mechanically coupled to the crankshaft by a freewheel (e.g., an overrunning clutch), such that torque is transmitted from the crankshaft to the driven shaft.
2. Description of the Related Art
In the development and advancement of internal combustion engines, attention in recent years has mainly been focused on minimizing pollutants and increasing the efficiency of the units. One possibility to increase efficiency in a modern internal combustion engine is to make optimum use of the heat generated in the area of the internal combustion engine. By taking appropriate measures, it is possible to limit the structural dimensions of the required cooling system and also to make the heat loss, which is otherwise merely given off into the environment, usable for other applications within the motor vehicle.
To improve engine cooling, combustion engines, have been developed such that the corresponding systems make it possible to utilize heat generated in the area of the combustion engine in the most efficient manner possible. In this connection, it is possible to use the occurring heat for other heatsinks provided in the motor vehicle or to convert the heat energy into mechanical energy, particularly kinetic energy, by means of corresponding cyclical processes.
US 2008/0223040 discloses a drive unit having an internal combustion engine mechanically connected to a piston engine. Wherein a fluid is evaporated in a separate work cycle by the waste heat from the combustion engine and the vapor is conducted into the cylinders of the piston engine, setting in motion the pistons which are movably mounted therein. In this way, a crankshaft of the piston engine, which is mechanically connected to the crankshaft of the internal combustion engine, is set in motion. It is therefore possible with the described system to make use of the waste heat of the internal combustion engine for transmitting torque to the crankshaft of the internal combustion engine by the piston engine.
Based on known design principles, there are basically two conceivable technical solutions for ensuring that the expander, in particular the piston engine, does not constitute an additional load that must be carried along in the warm-up phases of the heat recycling system.
Due to the short induction times when filling the cylinders, depending on accurate engine timing, given a quantity of 7 to 8 cylinders, there is always one intake valve open, and the expander starts by itself when vapor is available. In this case, the crankshaft of the self-starting expander is connected to the crankshaft of the internal combustion engine by a freewheel (overrunning clutch). This freewheel ensures that a transmission of torque occurs exclusively from the crankshaft of the expander to the crankshaft of the internal combustion engine. Once sufficient vapor is available to the cylinders from the heat recycling system, the expander performs work so that torque is transmitted to the crankshaft of the internal combustion engine.
In expanders that are provided in addition to an internal combustion engine and which are not self-starting due to a small number of cylinders, an appropriate clutch is provided in place of the freewheeling connection between the crankshaft of the expander and the crankshaft of the internal combustion engine. The availability of vapor from the heat recycling system is detected by a sensor arrangement and the clutch between the two crankshafts is closed so that the expander is dragged by the internal combustion engine until an intake valve of the expander opens and the expander starts.